1. Field of Use
This invention relates generally to hydraulic brake systems for the crane hoist drums or the like. In particular, it relates to a hydraulic brake system employing a brake cylinder for operating a brake band and a pedal-operated brake valve for controlling fluid flow to the brake cylinder.
2. Description of the Prior Art
Some machines, such as lift cranes, hoists, or the like, wherein a mechanical load is imposed on a cable drum, employ a hydraulic brake system in which a brake band is engagable with brake drums by means of a brake cylinder in response to operating of a pedal-operated brake valve.
It is current practice, on lifting cranes, to make adjustment to the drum brake band (loose or tight) to permit the brake cylinder to travel more or less to set brake. This in turn permits the pedal to travel more or less to provide required oil for cylinder. A "low" pedal being closer to toggle has a greater mechanical advantage over a "high" pedal. "Low" pedal is good for controlling heavy loads and a "high" pedal for light loads. Adjusting the band is very inconvenient and can also upset the original adjustment required for a safety spring loaded brake.
The prior art discloses many hydraulic brake control systems of the aforesaid and related character, as the below-mentioned patents indicate.
Graziano U.S. Pat. No. 2,153,042 discloses an oil replenishing device for a braking system that has no make-up oil as does a standard master cylinder. Oil may be required due to loss or required to set worn brake shoes. The replenishing device actually partially applies the brake shoes prior to foot pedal application. The replenishing device includes a spring which remains in a selected position while the brake pedal is applied and released. However, the replenishing device does not intermittently store active oil.
Weihe U.S. Pat. No. 2,085,620 shows a hydraulic system charging device used as a parking brake. However, it allows some oil leakage loss due to spring loading feature. Turning a knob on the charging device applies the brakes in a static condition.
The following patents on brake circuits limit the return oil volume from releasing the brakes, therefore, the volume of oil required to reset the brakes does not change due to brake wear: Brannen U.S. Pat. No. 2,588,955; Brueder U.S. Pat. No. 2,961,831; Guthmann U.S. Pat. No. 3,709,336; Montjourides U.S. Pat. No. 3,734,246; Schacher U.S. Pat. No. 3,819,021.
In regard to the prior art, a distinction must be noted between the hydraulic simulator hereinafter described and spring loaded hydraulic accumulators. A sring loaded hydraulic accumulator is one of many devices for storing hydraulic energy as a battery stores electrical energy. Applicant's simulator is not an energy device but is rather a volume or displacement receiving device with a manual adjustment which makes possible a predetermined volume of fluid to be received. The spring in Applicant's device does not absorb usable energy but merely restores the brake valve (master cylinder) to neutral after the braking work has been performed.